1. Field of the Invention
This invention pertains to the field of valves. More particularly it pertains to a shut-off valve used primarily in the filling of above-ground fuel tanks and to a unique combination of elements therein that permits smooth, safe control of the high pressure fuel flow that accompanies the filling of these tanks.
2. Description of the Prior Art
Fuel tanks have existed since the dawn of the industrial revolution. While many vehicles and machines operated from a self-contained fuel tank, these tanks must be repeatedly refilled to permit continued usage. The tanks, from which these smaller tanks are refilled, and the valving involved therewith is the subject of this invention.
Traditionally, fuel tanks have been buried in the ground. A number of reasons support this philosophy. First, the tank is located below the plane of most human activity and thus out of the path of most accidents, such as runaway vehicles, collapsing buildings, fires, spilled materials and the like. Secondly, the surrounding earth provides not only beneficial insulation against possible penetration by flying missiles but also energy insulation to prevent overheating or overcooling of the tank contents. Thirdly, in the unlikely event of tank failure, the contents would seek a lower level in the earth away from contact with the public.
An ever-growing feeling of public concern over how man impacts our planet has led to reconsideration of this third reason. Conclusive evidence now exists that tank leakage allows fuel and other liquids to spread over enormous sectors of earth poisoning drinking water, reducing the load bearing properties of some soils, toxifying some areas to the extent that horticulture potential is curtailed or eliminated, and allowing fuel and other noxious vapors to be emitted from the ground to the extent that human occupancy is threatened. Tank leakage is caused by numerous factors such as age, corrosion, earthquake, metal fatigue and the like. As a result, legislative activity now compels many businesses to utilize above-ground fuel and other liquid storage and cease all such below ground practices. The storage of volatile and highly flammable fuels such as gasoline and naphtha as well as other liquids such as acids, alkalis and monomers is now often required to be strictly an above-ground activity.
For the most part, the technology of fabricating and filling below-ground tanks has been used in above-ground tanks. That is to say, the wall construction, anchoring, and piping of the tanks has remained substantially the same. The entry way into the top of both types of tanks remains a 4-inch MPT pipe.
A significant difference, however, is required in the process to fill above-ground tanks over that of below-ground tanks. Below-ground tanks are generally gravity fed; i.e., the tanker truck pulls up to the feed pipe, a short length of 4-inch transfer hose is connected between the lower tanker outlet and the top tank inlet, that is flush with the surface of the ground, through a spring-loaded device called a "dry-break coupler", and gravity is used to force the liquid down into the tank in measured volume. A low pressure shut-off valve is inserted in the 4-inch feed pipe and mounted axially therebelow to terminate the fuel flow when the fuel is filled to the appropriate level.
These low pressure shut-off valves are actuated by floats, attached to a moveable valve stop, that float on the surface of the liquid in the tank. As the tank is filled, the float rises with the rising liquid surface and moves the valve stop toward a shut-off valve seat. At a preset level of fullness, the float causes the valve stop to bottom against the valve seat and shut off the incoming flow. The volumetric flow indicator stops, indicating the tank is full. The operator than closes the tanker truck outlet. Drain means, usually in the form of a spring-loaded bypass valve held closed by the flow of fuel, then opens under spring pressure to drain fuel, caught in the fuel line between the dry-break coupler and the closed valve, from the closed valve down into the tank.
In filling above-ground tanks, the short 4-inch transfer hose is replaced with a lighter but far longer 2-inch hose to reach tanks located a distance from where the tanker truck can be parked. A high pressure transfer pump is interconnected therewith to produce an output pressure between 75-125 psi to overcome the added friction of the longer, narrower hose and to give a fuel flow similar to that occurring with below-ground tanks. This fuel flow creates a higher velocity of liquid in the 2-inch hose that causes significant problems with the shut-off valve.
While in below-ground tanks the lower velocity of fuel, passing through the 4-inch line, allows the common valve stop to move progressively from its open position to its closed position against the valve seat, at the higher velocity in the 2-inch line the pressure of the fuel on the valve stop causes it to either be held open leading to over-filling of the tank or to slam down early onto the valve seat, causing premature closing of the valve before the desired degree of filling has been accomplished. Further, the slamming of the valve stop against the valve seat creates a dangerously large shock wave that travels up into the transfer hose to the pump, often causing bursting of the hose, damage to the pump, and fuel leakage at the hose connections.
In other below-ground tank operations, a shut-off valve is used that comprises a pair of "C"-shaped valve flaps that are slowly rotated by rods, attached to one or more annular floats, from an open to a closed position. When used in the high pressure filling of above ground-tanks, the pressure of the high velocity fuel creates a reverse bending moment on the inboard mating edges of the valve flaps causing them to remain open beyond the desired degree of tank filling so that the tank is often overfilled resulting in spillage of fuel on the ground to create a fire hazard as well as environmental damage.
The problem appears to be that prior art shut-off valves are not designed to handle the high flow rates and fuel pressures created by the high pressure pump used to fill above-ground tanks. The industry has been stymied by the problems in this area such that, to date, about the only shut-off valve useful in filling above-ground tanks are those where the valve has such a narrow opening through the valve body that these newly created forces can be somewhat controlled. Unfortunately, these smaller valves reduce fuel flow rates even further and increase handling costs, both of which present obstacles to the safe and efficient handling of fuel and other liquids.